Apparatus for truing grinding wheels



Nov. 19, 1968 H. E. MERRITT APPARATUS FOR TRUING GRINDING WHEELS 5Sheets-Sheet 1 Filed April 5, 1966 I nvenlor Henry E. Merritt y WMttomey;

Nov. 19, 1968 HEMERRWT 3,411,492

APPARATUS FOR TRUING GRINDING WHEELS Filed April 5,195 5 Sheets-Sheet 47Inventor Henry E. Merritt y M MW I WA Nov. 19, 1968 H. E. MERRITT3,411,492

APPARATUS FOR TRUING GRINDING WHEELS Filed April 5, 1966 5 Sheets-Sheet5 Inventor Henry E. Merritt A ttorney;

United States Patent Ofiice 3,411,492 APPARATUS FOR TRUING GRINDINGWHEELS Henry E. Merritt, Warwick, England, assignor to Merritt & Co.(Engineering) Limited, Warwick, England, a British company Filed Apr. 5,1966, Ser. No. 540,408 Claims priority, application Great Britain, Apr.10, 1965, 15,335 65 Claims. (Cl. 125-11) ABSTRACT OF THE DISCLOSURE Inapparatus for truing the profile of a grinding wheel the truing tool isadjustably mounted on a gimbals arrangement which is connected by auniversal joint to the follower of a cam and follower arrangement whichgenerates the form of the desired profile. Movement of the follower istransmitted to the truing tool by the universal joint so that, in use,the tool is maintained normal to the profile of the grinding wheel, andthe size of the profile reproduced by the truing tool may be varied byvirtue of the tool mounting being adjustably carried on the gimbalsarrangement. Grinding wheels for cutting internal and external gearteeth may be trued by the apparatus.

This invention relates to apparatus for truing grinding wheels,especially but not exclusively involute gear grinding wheels.

According to the present invention, there is provided apparatus fortruing grinding wheels to a desired profile, said apparatus including abase, a carrier rotatably mounted on the base about a carrier axis, afirst gimbal member rotatably mounted on the carrier about a firstgimbal axis, a second gimbal member rotatably mounted on said firstgimbal member about a second gimbal axis, said first and second gimbalaxes and said carrier axis intersecting at a point fixed relative tosaid base, a tool holder on said second gimbal member for holding agrinding wheel truing tool, and profile generating means including aguide fixed relative to said base, and a follower adapted to co-operatewith the guide so as to generate the form of the desired profile, and aconnection between the second gimbal member and the follower, saidconnection being adapted to transmit movement of the follower to saidsecond gimbal member so that the latter moves about said point, and thetip of a grinding wheel truing tool, when held on the tool holder, movesin a path which substantially corresponds with the desired profile.

An embodiment of the invention will now be described, by way of example,with reference to the accompanying drawings, in which:

FIG. 1 is a sectional side elevation of apparatus according to theinvention;

FIG. 2 is a plan corresponding to FIG 1, and

FIG. 3 is an end elevation corresponding to FIG. 1.

The apparatus shown in the drawings consists in general of a toolcarrying assembly connected to a profile generating assembly by auniversal type joint.

In the tool carrying assembly, a carrier 10 having spaced upwardlyextending arms is mounted on a stationary base 11 for rotation about avertical axis 12. At the upper ends of the arms of the carrier 10 thereis mounted a rectangular frame 13 which is rotatable on the arms about ahorizontal axis 14 which intersects the vertical axis .12 at a gimbalpoint 15 which is stationary.v

As can be seen in FIG. 2, the axis 14 is normal tothe length of theframe 13.

A movable member in the form of a bar 16 fits neatly 3,411,492 PatentedNov. 19, 1968 into the frame 13 and has a crank 17 at each end. The bar16 is parallel to the long side of the frame 13 and is journalled on theframe 13 for rotation about an axis 18 which passes through the gimbalpoint 15 and which is the longitudinal central axis of the rectangularframe 13. The relative sizes of the bar 16 and the frame 13 are suchthat the bar 16 may be rotated through 360 on the axis 18.

The bar 16 is rotatably mounted on the frame 13 by means of crank pins19, 20. The crank pin 20 extends through the frame 13 and has a controlball 21 on the end out with the frame 13. The centre of the control ball21 lies on the axis 18. A guide ball 22 is connected to the pin 20 andis spaced therefrom by an arm 22A so that a line joining the ballcentres is normal to the axis 18. Thus rotational movement of the guideball 22 about the axis 18 is transmitted to the bar 16 and transversemovement of the control ball 21 relative to the base 11 is transmittedto the bar 16. A tool holder 23 is s'lidably and adjustably mounted onthe inside of bar 16 and holds a tool 24 having a diamond point 25. Theaxis of the tool 24 is normal to the axis 18. The tool holder 23 can besecured in any position along the length of the bar 16 between the endcranks 17, and the tool 24 can be adjustably positioned in the toolholder 23 so that the diamond point 25 lies on the axis 18.

The tool holder 23 is. on the opposite side of axis 18 from the arm 22Aso that the axis of the tool 24 is parallel to the line joining the ballcentres.

Profile generating means for moving the bar 16 and hence the diamondpoint 25 consists of two guide plates 26, 27 bolted to the base 11. Theguide plates 26, 27 are slightly greater than semi-circular, are of thesame diameter and are mounted in a parallel spaced upright manner withtheir common axis 28 parallel to and directly below the axis 18. Astraight follower in the form of a rocking plate 29 rolls on the curvedsurfaces of the guide plates and is attached to said plates by means oftaut steel tapes 30. Each tape 30 is attached at one end to one of theguide plates 26, 27, contacts the curved surface of a guide plate,leaves the curved surface at the point of contact between the rockingplate 29 and the guide plate and thereafter contacts the rocking plate,the other end of the tape being attached to the end of the rockingplate.

There are four tapes 30 (two for each guide plate) and adjacent tapes 30are oppositely attached to the relative parts. The tapes 30 thusconstrain the rocking plate 29 to roll truly on the guide plates 26, 27.

A. T-shaped swivel arm 31 is positioned upright and a leg 32 of the Tpasses through a longitudinal slot 33 in the rocking plate 29 and theupper cross pieces 34 of the T arm carry rollers 35 which are engaged inlongitudinal grooves 36 in the rocking plate 29.

The lower end of the leg 32 is rotatable about a dowel pin 37 joiningthe guide plates 26, 27. The dowel pin 37 passes through a hole 38 inthe leg 32. The hole 38 is of larger diameter than the dowel pin 37.Below the dowel pin 37, the leg 32 has a bore 39 in which there is aspring-urged plunger 40 which has a concave end face corresponding tothe curvature of the dowel pin 37. The plunger 40 bears on the dowel pin37 and by reaction maintains contact between the rocking plate 29 andthe guide plates 26, 27. Thus, regardless of the angular position of theT-shaped arm 31, the rocking plate 29 and guide plates 26, 27 will bespring-urged towards each other.

In order to roll the rocking plate 29 on the guide plates 26, 27 thereis provided a rotatable crank 41 mounted on the guide plate 27, and thiscrank 41 has a roller 42 which neatly engages a longitudinal slot 43 inthe leg 32 of the T arm 31. The crank 41 is keyed to a worm wheelspindle 44 rotatable by a worm 45 and Wormwheel 46 contained in agearbox casing 47. The worm 45 may be rotated, manually or otherwise, bymeans of a square end 48 on the worm shaft 49 and which projects fromthe casing 47.

A connection between the two main parts of the apparatus is establishedby an adjustable setting block 50 releasably secured to a swivel head 51attached to the rocking plate 29 at the side remote from the worm andwormwheel casing 47. The swivel head 51 had a guideway extendingparallel to the rocking plate and on which the setting block 51 slides;the setting block 50 has a cylindrical socket 52 in which the controlball 21 neatly fits so that it can slide in the direction of the axis ofthe cylindrical socket 52. The guide ball 22 is located in a slot 53 inthe setting block 50. The length of the slot 53 is greater than thediameter of the guide ball 22, and the width of the slot 53 is equal tothe diameter of the ball 22, so that the line joining the ball centresremains parallel to the guideway on the swivel head 51. The swivel head51 comprises two relatively rotatable discs 54, 55 so that the guideball 22 and the bar 16 may be set at 180 relative to the position shownin FIG. 2.

The position of the apparatus in the drawings is the datum position andthe axis 18 passes through the tangent point between the rocking plate29 and the guide plates 26, 27. If it is desired to true an involutegear grinding wheel, the wheel is placed with the lower end of itsprofile touching the diamond point and with its axis of rotation normalto the axis 18. The wheel is rotated relatively quickly and then theworm 45 is also rotated. Thus the swivel arm 31 pivots from the verticalposition and the rocking plate 29 is induced to roll on the curvedsurfaces of the guide plates 26, 27. Therefore, in end elevation, FIG.3, the control ball 21 describes an involute to a base cylinder ofradius equal to that of the guide plates 26, 27. As the gimbal point 15,which is on the axis 18, is fixed, all points on the axis 18, in endelevation, describe involutes to base circles of varying radius. Thebase circle radius at the gimbal point is zero, and the base circleradius increases progressively as points on the axis 18 move furtherfrom the gimbal point 15. The guide ball 22 maintains the line joiningthe ball centres tangential to the base circle at all times, and,therefore, the axis of the tool 24 remains normal, in end elevation, tothe profile of the grinding wheel.

As the swivel arm 31 rotates, the diamond point trues the gear profileon the grinding Wheel, and the involute reproduced by the diamond point25 is reduced in relation to the involute of the control ball centre bythe ratio of the relative distances of the control ball centre and thediamond point 25 from the gimbal point 15.

In order to true a corresponding profile on the other side of thegrinding wheel the bar 16 is rotated through 180 and the swivel arm isrotated in the opposite direction by the worm and wormwheel 46.

Inverseinvolutes may be trued by moving the tool holder 23, with thediamond point 25 to the other end of the frame from that shown in thedrawings in order to true grinding wheels for producing internal teeth.

Dependent upon the characteristics of the gear to be produced by thegrinding wheel being trued, the position of the setting block may beadjusted relative to the guideway on the swivel head 51, in thedirection of the rolling surface of the rocking plate 29. Thisadjustment provides a means of varying the tooth thickness in the finalcut gearwheel.

Appropriate data for the grinding wheel will govern the position of thediamond point 25 on the axis 18 relative to the gimbal point 15.

The apparatus may be mounted on an extension of the bed of a grindingmachine so that the axis of the workpiece, the axis of the base cylinderand the gimbal point will all lie in the same vertical plane.

Whereas any point on the rocking plate 29 moves in a plane, the diamondpoint 25 moves on the surface of a sphere the centre of which is thegimbal point 15. In practice, however, the error due to the sphericalmovement of the diamond point 25 is negligible.

It will be realised that for a particular curvature of the guide plates26, 27 a limited range only of involutes may be generated. This can beovercome by providing a series of differently sized guide plates.

In a modification of the invention, not shown, the frame 13 isopen-sided in that it is U-shaped in plan and is rotatably supported ona single carrier arm for rotation about horizontal axis 14. In this casethe bar 16 would be rotationally displaced to a position below the planeof the frame 13. The diamond point 25 would, of course, remain on theaxis 18. The shape of the tool holder would have to be slightlymodified. Also, the inner ends of the pivot pins 19, 20, may be used forthe purpose of mounting a device for setting the diamond point to therequired position.

The apparatus may be used to true grinding wheels other than geargrinding wheels, for example milling cutter grinding wheels and splinegrinding wheels.

The invention need not necessarily be limited to truing involuteprofiles, and may be used to true any gear grinding wheel profile. Forexample, a profile generator may be used which produces circular arcs orother profiles dependent upon the shape of the guide and the manner inwhich the follower moves on the guide.

I claim:

1. Apparatus for truing grinding wheels to a desired profile, saidapparatus including a base, a carrier rotatably mounted on the baseabout a carrier axis, a first gimbal member rotatably mounted on thecarrier about a first gimbal axis, a second gimbal member rotatablymounted on said first gimbal member about a second gimbal axis, saidfirst and second gimbal axes and said carrier axis intersecting at apoint fixed relative to said base, a tool holder on said second gimbalmember for holding a grinding wheel truing tool, and profile generatingmeans including a guide fixed relative to said base, and a followeradapted to co-operate with the guide so as to generate the form of thedesired profile, and a connection between the second gimbal member andthe follower, said connection being adapted to transmit movement of thefollower to said second gimbal member so that the latter moves aboutsaid point, and the tip of a grinding wheel truing tool, when held onthe tool holder, moves in a path which substantially corresponds withthe desired profile.

2. Apparatus according to claim 1, in which the tool holder isposition-adjustably mounted on the second gimbal member.

3. Apparatus according to claim 2, in which the tool holder isselectively positionable on either side of the plane containing thecarrier axis and the first gimbal axis.

4. Apparatus as claimed in claim 3, in which the connection between thesecond gimbal member and the follower includes a universal jointcomprising a first balland-socket element for rotating said secondgimbal member about the second gimbal axis and a second balland-socketelement for causing displacement of said second gimbal axis relative tosaid base.

5. Apparatus as claimed in claim 4, in which the universal joint isposition-adjustably mounted on the follower.

6. Apparatus as claimed in claim 4, in which the balls of saidball-and-socket elements are in fixed mutual relationship and areconnected to said second gimbal member.

7. Apparatus as claimed in claim 6, in which an imaginary line passingthrough the ball centres of the first and second ball-and-socketelements in parallel to the axis of a grinding wheel truing tool whenthe latter is held in the tool holder.

8. Apparatus according to claim 7, in which the guide References Citedhas a cam surface and the arrangement is such that the UNITED STATESPATENTS follower ma roll on said cam surface.

9. Apparatus according to claim 8, in which said guide 1912410 6/1933shotfsy 125 11 has a cylindrical cam surface and the follower is a fiat5 1988895 1/1935 Godzlewskl 125-11 plate. FOREIGN PATENTS 10. Apparatusaccording to claim 9, in which said fol- 1,045,823 7 /1953 France loweris constrained to roll on said cylindrical carn sur- 253,089 5/1926Great Britain.

face by yieldably tensioned flexible tie means connected to the followerand t0 the guide. 10 HAROLD D. WHITEHEAD, Primary Examiner.

